I can tell you how I measure the blood pressure, first we need to grab the patient's arm with the handcuff. * make sure the two tubings (one connected with the arm, another one connected to the 血壓計) 要向手掌(手掌向上), then find the pulse ( you can use the聽筒/ feel it by your fingertip ), which is around the the arm's 摺位.Then put the 聽筒 right above the purse. then squeeze the pump until the mercury mark rises to around 180 mmHg (for those have hypertension) or ~150 mmHg (for those have normal blood pressure) *never make the mercury mark rises above 200 mmHg. Then 放氣 a little bit so that the mercury mark drops about 2 mmHg per second. When you hear the first heart bit sound, that is your systolic pressure(上壓) and when you can't hear any heartbit, then that's the diastolic pressure (下壓) reading. you can also search some paper which tells you how to mearsure blood pressure. Althought it sounds easy, it is quite difficult at all, I tried at least 10 times in order to hear the diastolic pressure (下壓) reading.
the normal range of the pressure should with 140(下壓) /90(下壓)
blood measurement is not that danger at all as I tried the 血壓計 when I was a year 2 biology student, but it will be safer if someone experienced teach you how to use that